I really agree with Mickeyrat's basic sentiment here. I was shocked when I read this thread and some of the posts people had made about how they would have handled a similar situation. However, I think some of Mickeyrat's post was a little jumping to conclusions or misdirected about the OP's situation. Perhaps it could have been because of all the responses where people said things like "I would've punched him" or "I would have told him to shut up" or "I would have pulled out my gun". And Mickeyrat may have gotten a little to into listing what not to do in a way that implied that the OP had actually done all those things (which they hadn't). But IMO they are all things that aren't good to do when someone has a problem with a person vaping in public. I really think it is important to explain what a vaporizer does when someone has an issue with it. Just because the guy in the coffee shop had heard of "e-cigarettes" does not mean he understood how they worked and that it is just water vapor (with a little PG or VG) being exhaled. I think it's really important to stay calm and polite - 2 wrongs don't make a right and definitely don't get anyone on our side, and even jerks can sometimes be forced to submit to logic when confronted with information and kindness when they were looking for/expecting either a fight or quivering submission.
ETA: If I fully informed someone of how vaping is different from smoking and not affecting them and they still wanted me to stop I would ask them why. If they still wanted me to stop I would. This is assuming that I am in an indoor public place and am the only one vaping or an outdoor place where smoking is strictly banned and/or others are stuck in close quarters with me out of necessity. In other situations I think I would play it by ear. But in general, if someone is bothered by something I am doing, whether or not it is forbidden, I will usually stop. Just being considerate. If I was, say, listening to music and my neighbour asked me to shut it off but I knew it wasn't above the maximum decibel level, I would shut it off. If I was standing too close to someone and they said they were allergic to my perfume I would move away, even though I was not doing anything that is banned or illegal. If someone didn't like my t-shirt and didn't want to look at it, well, that really depends on the t-shirt and where it was, but I would probably begrudgingly put on a sweater. When it comes to vaping it is a much more sensitive issue which can affect us all as vapers. Just because something is not banned or illegal doesn't mean we don't have to care about how anyone else feels about our behaviour. We can and should ask them why they feel that way and explain ourselves, but it's not ridiculous for some of us to think it's in the vaping community's best interest to put our PVs away if asked.